path: root/src/selection_pipe.zig

//! Native runner and boundary-owned values for `|`: pipe every editor
//! selection through one shell command. The core imports only the plain value
//! types below; native shells call `Job.copy` before starting a worker, then
//! `runOne` on that worker. No subprocess or borrowed core memory reaches the
//! editor/event-loop thread.
const std = @import("std");
const filesystem = @import("fs.zig");

/// A deliberately finite answer. One selection cannot retain more than 1 MiB
/// and a multi-selection command cannot retain more than 4 MiB in total.
/// stderr is diagnostic-only and has a smaller independent ceiling. Crossing
/// any ceiling fails the whole atomic request.
pub const max_stdout_bytes: usize = 1024 * 1024;
pub const max_total_stdout_bytes: usize = 4 * 1024 * 1024;
pub const max_stderr_bytes: usize = 64 * 1024;
pub const command_timeout_seconds: u64 = 10;

pub const Input = struct { bytes: []const u8 };

/// Borrowed view exposed by the core while an effect is being drained.
pub const Request = struct {
    id: u32,
    command: []const u8,
    cwd: []const u8,
    inputs: []const Input,
};

/// Worker-owned snapshot. `copy` is intentionally called synchronously while
/// draining the effect: the worker can start after arbitrary later edits and
/// still owns exactly the command, directory, and selection bytes submitted.
pub const Job = struct {
    id: u32,
    command: []u8,
    cwd: []u8,
    inputs: [][]u8,

    pub fn copy(gpa: std.mem.Allocator, request: Request) !*Job {
        const job = try gpa.create(Job);
        errdefer gpa.destroy(job);
        job.* = .{
            .id = request.id,
            .command = try gpa.dupe(u8, request.command),
            .cwd = &.{},
            .inputs = &.{},
        };
        errdefer gpa.free(job.command);
        job.cwd = try gpa.dupe(u8, filesystem.localPath(request.cwd) orelse request.cwd);
        errdefer gpa.free(job.cwd);
        job.inputs = try gpa.alloc([]u8, request.inputs.len);
        errdefer gpa.free(job.inputs);
        var made: usize = 0;
        errdefer for (job.inputs[0..made]) |input| gpa.free(input);
        for (request.inputs, 0..) |input, i| {
            job.inputs[i] = try gpa.dupe(u8, input.bytes);
            made += 1;
        }
        return job;
    }

    pub fn deinit(job: *Job, gpa: std.mem.Allocator) void {
        gpa.free(job.command);
        gpa.free(job.cwd);
        for (job.inputs) |input| gpa.free(input);
        gpa.free(job.inputs);
        gpa.destroy(job);
    }
};

/// WHY a filter produced nothing, carried home so somebody can be told.
///
/// Until this existed the runner read the command's stderr into memory and
/// then FREED IT UNREAD — the one artifact that explains a failure, discarded
/// two lines after it arrived — and every caller answered a failed filter with
/// a bare `return`. `| trr a-z A-Z` (a typo), `| grep nomatch` (exit 1),
/// `| jq .` on bad JSON: all of them did nothing, said nothing, and left the
/// text alone with no way to find out why.
pub const Failure = struct {
    pub const Kind = enum {
        /// The command never started: no `/bin/sh`, a cwd that is gone, a NUL
        /// in the command, a fork that failed.
        spawn,
        /// Still running at `command_timeout_seconds`.
        timeout,
        /// Past `max_stdout_bytes` / `max_stderr_bytes` / the job total.
        too_large,
        /// Ran, and exited nonzero. `code` says which.
        exit,
        /// Killed by a signal.
        signal,
        /// A read, a write or an allocation failed under us.
        io,
    };

    kind: Kind = .io,
    /// Which selection this was, so a report over several cursors can say.
    index: u32 = 0,
    /// The exit status, when `kind` is `.exit`.
    code: u8 = 0,
    /// stderr exactly as the command wrote it, OWNED by the response. Empty
    /// when the command said nothing, which is why `kind` and `code` exist.
    stderr: []u8 = &.{},
};

/// One worker answer. `outputs` owns each slice; a failure owns an empty list
/// and, usually, the command's own account of itself in `failure`.
pub const Response = struct {
    id: u32,
    success: bool,
    outputs: [][]u8,
    failure: ?Failure = null,

    pub fn deinit(response: *Response, gpa: std.mem.Allocator) void {
        for (response.outputs) |output| gpa.free(output);
        if (response.outputs.len > 0) gpa.free(response.outputs);
        if (response.failure) |f| if (f.stderr.len > 0) gpa.free(f.stderr);
        response.* = undefined;
    }
};

/// What one invocation came to: the bytes, or the reason there are none.
pub const Outcome = union(enum) { ok: []u8, failed: Failure };

/// The in-flight set a host keeps while pipes run off its loop.
///
/// tty.zig and gui.zig each had this verbatim — same `finish` walk, same
/// `cancelAll`, same 16 — differing only in whether `add` asserted or returned
/// a bool. It lives here beside the Job it tracks so a third host (the AppKit
/// shell, which had no pipe support at all) does not have to grow a fourth.
///
/// Bounded on purpose: a filter is a user gesture, and sixteen concurrent ones
/// is already more than anybody means. `add` returning false is the host's cue
/// to answer the request as failed rather than to queue it.
pub const Tasks = struct {
    pub const capacity = 16;

    pub const Task = struct {
        id: u32,
        future: std.Io.Future(anyerror!void),
    };

    items: [capacity]Task = undefined,
    len: usize = 0,

    pub fn full(tasks: *const Tasks) bool {
        return tasks.len == tasks.items.len;
    }

    pub fn add(tasks: *Tasks, task: Task) bool {
        if (tasks.full()) return false;
        tasks.items[tasks.len] = task;
        tasks.len += 1;
        return true;
    }

    /// Join the one that answered and drop it, preserving order so `cancelAll`
    /// stays deterministic.
    pub fn finish(tasks: *Tasks, io: std.Io, id: u32) void {
        for (tasks.items[0..tasks.len], 0..) |*task, i| if (task.id == id) {
            task.future.await(io) catch {};
            tasks.len -= 1;
            std.mem.copyForwards(Task, tasks.items[i..tasks.len], tasks.items[i + 1 .. tasks.len + 1]);
            return;
        };
    }

    pub fn cancelAll(tasks: *Tasks, io: std.Io) void {
        for (tasks.items[0..tasks.len]) |*task| task.future.cancel(io) catch {};
        tasks.len = 0;
    }
};

const WriterContext = struct {
    io: std.Io,
    file: std.Io.File,
    input: []const u8,
    ok: bool = false,
};

fn writeInput(context: *WriterContext) void {
    defer context.file.close(context.io);
    context.file.writeStreamingAll(context.io, context.input) catch return;
    context.ok = true;
}

/// Run one POSIX shell command with exact stdin, concurrently draining stdout
/// and stderr so a producer cannot deadlock against a full pipe. The caller is
/// already a worker. Nonzero exit, signal, timeout, IO failure, or either
/// output ceiling is reported as `null`; only an exited-zero command transfers
/// ownership of stdout to the caller.
pub fn runOne(
    gpa: std.mem.Allocator,
    io: std.Io,
    command: []const u8,
    cwd: []const u8,
    input: []const u8,
) Outcome {
    const fail = struct {
        fn k(kind: Failure.Kind) Outcome {
            return .{ .failed = .{ .kind = kind } };
        }
    };
    if (std.mem.indexOfScalar(u8, command, 0) != null or
        std.mem.indexOfScalar(u8, cwd, 0) != null) return fail.k(.spawn);

    // std's spawn runs no code in the child: this thread's mask, which the
    // child inherits, is cleared across the fork (only the tty's SIGWINCH is
    // ever blocked, and its default is to be ignored). A handler resets at
    // exec by itself, and nothing here is ignored.
    const none = std.posix.sigemptyset();
    var kept: std.posix.sigset_t = undefined;
    std.posix.sigprocmask(std.posix.SIG.SETMASK, &none, &kept);
    defer std.posix.sigprocmask(std.posix.SIG.SETMASK, &kept, null);
    var child = std.process.spawn(io, .{
        .argv = &.{ "/bin/sh", "-c", command },
        .cwd = if (cwd.len == 0) .inherit else .{ .path = cwd },
        .stdin = .pipe,
        .stdout = .pipe,
        .stderr = .pipe,
    }) catch return fail.k(.spawn);

    var writer_context: WriterContext = .{
        .io = io,
        .file = child.stdin.?,
        .input = input,
    };
    child.stdin = null; // writer_context owns and closes this endpoint
    var writer: ?std.Thread = std.Thread.spawn(.{}, writeInput, .{&writer_context}) catch {
        writer_context.file.close(io);
        child.kill(io);
        return fail.k(.spawn);
    };
    // On every early return kill first, unblocking a command which never read
    // stdin, then join the short-lived writer before its borrowed input dies.
    defer if (writer) |thread| thread.join();
    defer child.kill(io);

    var multi_reader_buffer: std.Io.File.MultiReader.Buffer(2) = undefined;
    var multi_reader: std.Io.File.MultiReader = undefined;
    multi_reader.init(gpa, io, multi_reader_buffer.toStreams(), &.{ child.stdout.?, child.stderr.? });
    defer multi_reader.deinit();

    const stdout_reader = multi_reader.reader(0);
    const stderr_reader = multi_reader.reader(1);
    const deadline: std.Io.Timeout = (std.Io.Timeout{ .duration = .{
        .clock = .awake,
        .raw = .fromSeconds(command_timeout_seconds),
    } }).toDeadline(io);
    while (multi_reader.fill(64, deadline)) |_| {
        if (stdout_reader.buffered().len > max_stdout_bytes or
            stderr_reader.buffered().len > max_stderr_bytes) return fail.k(.too_large);
    } else |err| switch (err) {
        error.EndOfStream => {},
        // The deadline is the only one of these a human is likely to cause,
        // and it is the one they are least able to guess at: ten seconds of
        // nothing used to be followed by nothing.
        error.Timeout => return fail.k(.timeout),
        else => return fail.k(.io),
    }
    if (stdout_reader.buffered().len > max_stdout_bytes or
        stderr_reader.buffered().len > max_stderr_bytes) return fail.k(.too_large);
    multi_reader.checkAnyError() catch return fail.k(.io);
    const term = child.wait(io) catch return fail.k(.io);
    writer.?.join();
    writer = null;

    const stdout = multi_reader.toOwnedSlice(0) catch return fail.k(.io);
    const stderr = multi_reader.toOwnedSlice(1) catch {
        gpa.free(stdout);
        return fail.k(.io);
    };
    // stderr is NOT freed here any more. It is the command's own account of
    // what went wrong, and it goes home with the failure.
    errdefer gpa.free(stderr);

    // A STDIN WRITE THAT ENDED EARLY IS NOT A FAILURE. `writer_context.ok` was
    // part of this condition, so `| head -1` over a selection bigger than the
    // pipe buffer failed — the command closed stdin after the line it wanted,
    // the write got EPIPE, and a filter that had done exactly its job reported
    // nothing. helix joins its input task and ignores the result for this
    // reason; the exit status is the whole verdict.
    switch (term) {
        .exited => |code| if (code != 0) {
            gpa.free(stdout);
            return .{ .failed = .{ .kind = .exit, .code = code, .stderr = stderr } };
        },
        else => {
            gpa.free(stdout);
            return .{ .failed = .{ .kind = .signal, .stderr = stderr } };
        },
    }
    gpa.free(stderr);
    return .{ .ok = stdout };
}

/// Invoke the command independently for every selection. The response is all
/// or nothing: one failure frees every earlier stdout and returns a failed,
/// empty answer for the core to ignore.
pub fn runJob(gpa: std.mem.Allocator, io: std.Io, job: *const Job) Response {
    var response: Response = .{ .id = job.id, .success = false, .outputs = &.{} };
    const outputs = gpa.alloc([]u8, job.inputs.len) catch return response;
    var made: usize = 0;
    var total: usize = 0;
    for (job.inputs, 0..) |input, i| {
        const output = switch (runOne(gpa, io, job.command, job.cwd, input)) {
            .ok => |bytes| bytes,
            .failed => |f| {
                // WHICH selection, because with several cursors "it failed" is
                // not enough to go looking with.
                var owned = f;
                owned.index = @intCast(i);
                response.failure = owned;
                break;
            },
        };
        if (std.math.add(usize, total, output.len) catch null) |next_total| {
            if (next_total <= max_total_stdout_bytes) {
                outputs[i] = output;
                total = next_total;
                made += 1;
                continue;
            }
        }
        gpa.free(output);
        response.failure = .{ .kind = .too_large, .index = @intCast(i) };
        break;
    }
    if (made != job.inputs.len) {
        for (outputs[0..made]) |output| gpa.free(output);
        gpa.free(outputs);
        return response;
    }
    response.success = true;
    response.outputs = outputs;
    return response;
}

test "native selection filters use the physical directory of an explicit OS mount" {
    const gpa = std.testing.allocator;
    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();
    var directory_buf: [4096]u8 = undefined;
    const directory = directory_buf[0..try tmp.dir.realPath(std.testing.io, &directory_buf)];
    var declared_buf: [4102]u8 = undefined;
    const declared = try std.fmt.bufPrint(&declared_buf, "/n/os{s}", .{directory});
    const job = try Job.copy(gpa, .{ .id = 1, .command = "pwd", .cwd = declared, .inputs = &.{.{ .bytes = "" }} });
    defer job.deinit(gpa);
    try std.testing.expectEqualStrings(directory, job.cwd);
    switch (runOne(gpa, std.testing.io, job.command, job.cwd, "")) {
        .ok => |bytes| {
            defer gpa.free(bytes);
            try std.testing.expectEqualStrings(directory, std.mem.trimEnd(u8, bytes, "\n"));
        },
        .failed => |failure| {
            gpa.free(failure.stderr);
            return error.FilterFailed;
        },
    }
}

test "native pipe runner preserves stdin/stdout bytes and reports how it failed" {
    const gpa = std.testing.allocator;
    const io = std.testing.io;
    const output = switch (runOne(gpa, io, "printf 'prefix:'; cat; printf '\\n'", "/tmp", "a\x00b\n")) {
        .ok => |bytes| bytes,
        .failed => return error.PipeCommandFailed,
    };
    defer gpa.free(output);
    try std.testing.expectEqualSlices(u8, "prefix:a\x00b\n\n", output);

    // A NONZERO EXIT COMES HOME WITH ITS REASON. The status and the command's
    // own stderr are the whole of what a human needs to fix a typo'd filter,
    // and both used to be freed on the floor.
    switch (runOne(gpa, io, "echo trouble >&2; exit 7", "/tmp", "")) {
        .ok => |bytes| {
            gpa.free(bytes);
            return error.PipeShouldHaveFailed;
        },
        .failed => |f| {
            defer gpa.free(f.stderr);
            try std.testing.expectEqual(Failure.Kind.exit, f.kind);
            try std.testing.expectEqual(@as(u8, 7), f.code);
            try std.testing.expectEqualSlices(u8, "trouble\n", f.stderr);
        },
    }

    // ...and a command that stops reading its stdin SUCCEEDS. `| head -1` over
    // a selection bigger than the pipe buffer takes the line it wanted and
    // closes the pipe; the write gets EPIPE, and that used to fail the filter
    // even though it had done exactly its job.
    const big = try gpa.alloc(u8, 512 * 1024);
    defer gpa.free(big);
    @memset(big, 'x');
    big[0] = 'a';
    big[1] = '\n';
    switch (runOne(gpa, io, "head -1", "/tmp", big)) {
        .ok => |bytes| {
            defer gpa.free(bytes);
            try std.testing.expectEqualSlices(u8, "a\n", bytes);
        },
        .failed => return error.EarlyStdinCloseShouldNotFail,
    }
}